Daniel Vérité, who was responsible for the Amiga port of Adebug - surely the most powerful debugger on Atari ST, just released the source code of his port under the GPL v2 licence.
You can find it on github : https://github.com/dverite/adebug-amiga.
You can find my current Atari release, patched to support the 68060 on my github: https://github.com/frost242/adebug. I didn't take a deep look at it, but it may interest some people here.